Method for producing thread roll dies

ABSTRACT

A method for making a thread roll die which is adapted to roll a single continuous pitch thread having two dissimilar thread form sections on a cylindrical bolt blank. A crusher roll having two groups of equally spaced ridges and grooves on its cylindrical surface is pressed against, and rolled over, the top surface of a pair of spaced die blanks. The blanks are positioned at an angle to the path of travel of the roll which is equal to the lead angle of the threads to be rolled and each blank is associated with the only one of the groups of the ridges and grooves on the crusher roll. As the crusher roll is moved over the blanks a complementary pattern of ridges and grooves is formed on each blank by each of the groups. After the rolling operation is completed, the blanks are clamped together along adjacent sides to form a completed unitary thread roll die.

United States Patent Carpenter et al.

[ 1 Feb.1,l972

[72] Inventors: Mark Richard Carpenter, Oreland; Albert P. Ludwig, Richboro, both of Pa.

Standard Pressed Steel Co., Jenkintown, Pa.

[22] Filed: Sept. 4, 1970 [21] Appl.No.: 69,873

[73] Assignee:

[56] References Cited UNITED STATES PATENTS 3,044,329 Seibert ..76/l0l B X FOREIGN PATENTS OR APPLICATIONS 384,949 l2/l932 Great Britain ,.76/l0l B Primary ExaminerBemard Stickney Attorney-Andrew L. Ney

[5 7] ABSTRACT A method for making a thread roll die which is adapted to roll a single continuous pitch thread having two dissimilar thread form sections on a cylindrical bolt blank. A crusher roll having two groups of equally spaced ridges and grooves on its cylindrical surface is pressed against, and rolled over, the top surface of a pair of spaced die blanks. The blanks are positioned at an angle to the path of travel of the roll which is equal to the lead angle of the threads to be rolled and each blank is associated with the only one of the groups of the ridges and grooves on the crusher roll. As the crusher roll is moved over the blanks a complementary pattern of ridges and grooves is formed on each blank by each of the groups. After the rolling operation is completed, the blanks are clamped together along adjacent sides to form a completed unitary thread roll die.

1 1 Claims, 6 Drawing Figures PATENTEU FEB narz 3,638,514

mm 1 8F 2 INVENI'ORS MARK RICHARD CARPENTER ALBERT P. LUDWIG AT ORNEYS METHOD FOR PRODUCING THREAD ROLL DIES This invention relates to a method for making a thread roll die and in particular to a method for making a die which is used to roll thread forming screws.

Thread-forming screws rolled by dies formed by the method of this invention are similar to those disclosed in copending U.S. Pat. application Ser. No. 802,774, filed Feb. 27, 1969, now Pat. No. 3,527,136, issued Sept. 8, 1970, which disclosure is incorporated herein by reference. In brief, that application describes a thread forming screw which includes a shank portion having a pilot end adapted to be received in an unthreaded hole in a metallic member. The screw includes a continuous constant pitch thread having a truncated form on its pilot end, and a full form on the remainder of the shank. Protruding from the truncated thread form are a plurality of cam-shaped thread-forming members which initially align the screw within the unthreaded hole and, as the screw is rotated, roll form an internal thread configuration in the hole. In this manner, the hole in the metallic member is threaded and then engages and retains the full form threads of the screw as it is rotated within the threaded hole.

One method of forming screw threads of this type involves the use of the thread roll dies described in our copending U.S. Pat. application Ser. No. 69,689, filed Sept. 4, 1970, the disclosure of which is incorporated herein by reference.

The dies described therein are generally rectangular, longitudinally extending plates having serrations on one face thereof which serrations are inclined with respect to the longitudinal axis of the die at an angle corresponding to the lead angle of the threads to be rolled on a cylindrical blank. The serrations include alternate peaks and grooves which run the length of the die face and conform substantially to the shape of the threads to be rolled on the blank. Accordingly, the crests of all the ridges lie in a common horizontal plane and serve to form the thread roots and the depth of the grooves between the ridges in one generally rectangular portion of the die is greater than the depth of the grooves between the ridges in the remaining generally rectangular portion of the die so that the deeper grooves serve to form the full thread form on the blank and the remaining grooves serve to form the truncated thread form. Arcuate cavities of various depths are formed in the shallower grooves of the die to define the complement of the cam-shaped thread-forming protuberances or lobes which are to be rolled on the truncated thread form. The spacing between ridges is the same in both portions of the die so that the thread formed on the blank has a constant pitch.

When using the dies described in our copending application, the cylindrical blank is placed between opposed complementary dies at one end thereof. One of the dies is then pressed against the blank and moved longitudinally, thereby rotating the blank about its axis and roll forming the screw thread.

In the past, thread rolling dies for rolling a single thread form have been formed by the use of a crusher roll which includes a plurality of annular ridges and grooves on its cylindrical surface. By pressing the crusher roll against one surface of a die blank at an angle to the blanks longitudinal axis, which angle corresponds to the desired lead angle of the thread to be formed, and by rolling the crusher roll along that surface, complementary serrations are formed on the die blank. The use of crusher roll die forming methods has heretofore been unsuitable for making thread rolling dies for fonning a single, continuous pitch thread having dissimilar thread form sections because of the fact that during the rolling operation each point on the bolt blank rolls along the die in a plane extending through a longitudinally extending line. Accordingly, in order to form a smooth transition thread on the bolt between the dissimilar thread forms, the transitions on the die face between the groove portions of different depth must all occur along a single line parallel to the longitudinal axis of the die; but, prior to the this invention, crusher roll die forming methods could not form the transition between groove portions of different depths along a single longitudinally extending line. As a result,

the manufacture of dies having constant pitch thread with dissimilar thread forms would require hand engraving the die blank or other expensive techniques.

Accordingly, it is an object of the present invention to provide an economical method for making thread rolling dies which can roll a single constant pitch thread on bolts with dissimilar thread fonn sections. Another object of this invention is to provide an economical method for making thread rolling dies which are adapted to roll a single constant pitch thread on bolts with a truncated thread form at one end having camshaped thread rolling members thereon. A still further object of the invention is to provide a method for making thread rolling dies of the character described which is relatively simple in operation, and highly accurate and efficient in use.

In accordance with one embodiment of the present invention, a crusher roll is provided which has a plurality of groups of evenly spaced annular ridges and grooves. Each group extends throughout the circumference of the roll and defines a different thread form corresponding to the thread forms to be rolled on a bolt blank. Since, in use, the crusher roll is adapted to rotate about its longitudinal axis, each group has a separate traverse path defined by the axial extent of each group. If camshaped lobes are to be formed on one of the thread forms, one of the groups should be formed with corresponding camshaped lobes.

A plurality of generally rectangular-shaped die blanks are placed adjacent each other so, that one blank lies in each traverse path and at an angle to each traverse path which corresponds to the desired lead angle of the threads to be formed on the bolt blank. Adjacent blanks are spaced so that no part of either die blank lies in the adjacent traverse path and, as will be explained more fully below, the spacing must be a whole number multiple of the pitch, that is, the distance between adjacent ridges. The crusher roll is then pressed against the top surface of each of the blanks and rolled therealong to cold-form serrations in the blanks which are complementary to the ridges, grooves and lobes on the crusher roll.

Since each blank lies in only one traverse path, each is engaged by only one of the groups of ridges and grooves on the roller, and thus dissimilar serrations are formed on each blank. After rolling, the blanks are then moved transversely and clamped in abutting relation with each other. Due to the even spacing of the ridges, the serrations on each plate will be aligned and the parallel adjacent sides of the blanks will define a straight line at which the transition between dissimilar serrations occurs. In this manner, a die is formed which is adapted to roll a single continuous thread with dissimilar threads forms on a cylindrical blank.

Further objects and advantages of the present invention will become apparent from the following description when considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a plan view of the crusher roll and spaced die blanks used in practicing the method of the present invention;

FIG. 2 is an enlarged plan view of a portion of the crusher roll illustrated in FIG. 1; l

FIG. 3 is a diagrammatic plan view of the assembled die;

FIG. 4 is a section view of the die taken along the line 4-4 of FIG. 3;

FIG. 5 is a plan view of the bolt formed by the die of FIG. 3; and

FIG. 6 is a view similar to FIG. 1 modified crusher roll used in practicing the method of the present invention.

With reference now to the drawings and in particular to FIG. 1, there is shown a generally cylindrical crusher roll 10 and a pair of spaced generally rectangular die blanks l2 and 14 positioned for engagement by the crusher roll. As will be more fully explained hereinafter, crusher roll 10 is pressed against the upper surface of blanks l2 and I4 and rolled longitudinally in the direction T, to cold-work the blanks and form a complementary serrated configuration thereon. Blanks l2 and 14 are then joined along their adjacent edges 16 and I8 to form the unitary thread rolling die 30 illustrated diagrammatically in FIG. 3.

The thread rolling die 30, thus formed, is used to roll form a thread forming screw 40, shown in FIG. 5. Screw 40 is similar to the screw disclosed in the above-noted US. Pat. application Ser. No. 802,774, and includes a head 42 and a shank 44 having a continuous thread 46. Shank 44 includes a pilot end 45 of reduced diameter and thread 46 includes a truncated form 48 on the pilot end and a full form 49 on the remainder of the shank. A smooth transition thread portion 47 is also provided between the two thread forms 48 and 49.

Extending radially outwardly from truncated thread form 48 and spaced inwardly from end 41 of shank 44 are camshaped protrusions or lobes 50, 50, 52 and 54 which are adapted to engage the wall of an unthreaded bore or hole in a workpiece (not shown) to roll form an internal thread configuration therein.

Truncated threads 48 have a slightly smaller diameter than the hole in which the thread rolling screw 40 is to be placed and the first few threads are smooth to facilitate insertion of the screw in the hole. Once the fastener member 40 has been placed in the unthreaded hole, it is rotated, thus causing the first camshaped lobes 50 and 50' to engage the wall of the hole. Lobes 50 and 50' are of like size and serve to score and partially form a mating thread configuration in the inner surface of the hole and to axially align the screw therein so that it is coaxial with the hole. As the screw is progressively engaged with the bore, the progressively large protrusions 52 and 54 successively engage the internal surface of the hole and follow and enlarge the scored indentation formed by lobes 50 and 50'. All of the lobes are oriented along the leadline of the threads to be formed to assure that the scoring always follows the same spiral. The progressively increasing size of the lobes permit a gradual scoring and engagement with the inner surface of the bore to facilitate plastic deformation of that surface.

The thread rolling die 30, shown in FIGS. 3 and 4, formed by the method of the present invention and adapted to roll form screw 40 described above, is similar to that disclosed in copending application (SPS Disclosure 491) and comprises plates 12 and 14 which are clamped together along their adjacent sides 16 and 18 by bolts 17. On one face of each plate there are a plurality of serrations that include ridges 60 and grooves formed between adjacent ridges. Each ridge 60 has a crest portion 61 and each of these crests lie in a common horizontal plane and form the complement of the roots of thread forms 48 and 49 on bolt 40. Adjacent ridges 60, formed on plate 14, define grooves 62 which are complementary to the full thread form 49 on screw 40 and adjacent ridges 60 on plate 12 define grooves 64, which are complementary to the truncated thread form 49 on screw 40.

Each of the ridges and grooves on die 30 is inclined at an angle a with respect to the longitudinal axis of the assembled plates which angle corresponds to the lead angle of the thread forms on the bolt. In addition, grooves 62 and 64 in each plate are aligned so that a single, continuous pitch thread is formed on the screw blank as the blank is rolled between complementary dies. As the screw blank is thus rolled, any point on its surfaces moves in a plane parallel to the longitudinal axis of the die and, accordingly, the junction of plates 12 and 14, along sides 16 and 18 and between aligned grooves of dissimilar depths, forms the smooth transition thread portion 47 between thread forms 45 and 49 on screw 40.

Certain of the grooves 64 on plate 12 are formed with sets of cavities 70, 70', 72 and 74 which are complementary to the lobes 50, 50', 52 and 54, respectively, formed by die 30 on screw 40. For convenience, each of the cavities in a set is indicated by the subscript a, b, or c. Each of the cavities in a set has a depth h, note FIG. 4, which substantially corresponds to the height of its complementary lobe on screw 40. Adjacent cavities in a set have their centers aligned and equally spaced along a line parallel to the longitudinal axis of the die. The spacing between the centers of each of the cavities in a set is substantially equal to the circumference of the cylindrical screw blank to be rolled, so that as the blank is rolled between mating dies, a lobe formed in the first cavity of a set, 74a for example, will mate with a similar complementary cavity 741) as the lobe is again rolled into contact with the die on its next revolution and again with cavity 740, on the final revolution. The use of a series of cavities to form a single lobe serves to accommodate and finish form the lobe initially formed in the first cavity.

In practice, to roll a thread on a cylindrical blank member, a pair of complementary dies are placed substantially parallel to each other in overlapped relationship sothat one die is leading and the other is trailing. A cylindrical blank is placed between the dies which are than pressed towards each other to compressively contact thecylindrical blank. The leading die is held stationary and the trailing die is moved longitudinally, thereby rolling the cylindrical blank about its longitudinal axis. The movement of the die in conjunction with the compressive force exerted on the blank causes the material of the blank to flow into the groove portions and cavities of the dies and out of the ridge portions thereof, to thus form the dissimilar thread configurations and cam-shaped protuberances on the blank. The flow of material in the bolt blank is actually threefold with the main portion of the material flow being along the helix angle formed by the inclined ridges and grooves. Another portion of the material flows into the grooves of the die and there is also a portion of the material which flows upwardly toward the top of the die. The head or tool-engaging end 42 of screw 40 is formed in a separate operation before the thread-forming process.

To assure that the lobes on the bolt are formed to their full height, it has been found that the upward and helical flow of material may be advantageously utilized by providing a flat zone 66 in plate 12 in the area immediately adjacent the first cavities contacted by the bolt, that is, cavities 74a and 70a. Accordingly, no thread forming will occur on the screw blank in the vicinity of the desired lobes until the blank engages the first cavities. Prior to the engagement of the blank with the first cavities, the material on the blank flowing helically and upwardly will accumulate on the face of the blank in the area where the lobes are to be formed. The accumulated material, along with the blank material normally present, will then be forced into the first cavities and form the cam-shaped lobes on the bolt. Zone 66 is formed on the same plane as grooves 64 and is provided by interrupting certain of the ridges 60 as seen in FIG. 3. These interrupted ridges are provided with smooth downwardly tapered transition portions 68 leading into and out of zone 66.

The completed unitary die is formed as previously noted, by cold-rolling die blanks l2 and 14 with crusher roll 10. More specifically, and with particular reference to FIG. 1 of the drawing, crusher roll 10 is mounted on a conventional mounting means (not shown) for rotation about its longitudinal axis 11 and for movement over blanks l2 and 14 in lateral direction indicated in the drawing by the arrow T. Two groups, and 82, of annular evenly spaced ridges are formed on the cylindrical surface 84 of roll 10 and each group defines a traverse path 86 and 88, respectively. Moreover, the ridges of one group differ in form from the ridges of the other group and as will be explained hereinafter, the ridges in the one group correspond to one thread form to be rolled on the bolt and the ridges in the other group correspond to the other thread form to be rolled on the bolt. Die blanks 12 and 14 are placed parallel to and spaced from each other in paths 86 and 88, respectively, and are positioned at an angle a to the direction of travel of roll 10. Angle a corresponds to the desired lead angle of the thread forms to be rolled on the screw blank so that as roll 10 cold-works die blanks l2 and 14, the complementary ridges 60 and grooves 62 and 64 are formed on the blanks at an angle a to the longitudinal axis of the blanks.

The spacing between the flat parallel sides 16 and 18 of blanks 12 and 14 is predetermined distance d chosen so that each die lies only in its associated traverse path. The minimum dimension for spacing d is determined by the equation d =L tan a, where L is the length of blank 12. As seen in FIG. 1, when d has this minimum dimension, each blank can be located entirely in its respective path, and each blank will only be contacted by the group of ridges 80 or 82 associated with its respective path. As more fully explained hereinafter, the dimension of space d must also be a multiple of the pitch, i.e., the spacing between adjacent ridges on roll 10.

Die blanks 12 and 14 include a pair of transversely aligned threaded bores 13 and 15, as seen in FIG. 1. Bolts 17 (note FIG. 4) are threadedly engaged in each of these bores and thus clamp the two blanks together to form an integral die unit 30. Prior to the crusher rolling operation bolts 17 are loosened to separate the die blanks 12 and 14 and a pair of hollow spacer blocks 90 are inserted between sides 16 and 18 and concentric with bores 13 and 15. Blocks 90 have a length equal to the predetermined dimension of spacing d and serve as a convenient gauge means. By tightening bolts 17 with the spacers 90 positioned between blanks 12 and 14 and around the bolts, the required relative positions and spacing of the die blanks are achieved and maintained, and the entire assembly may then be readily positioned in traverse paths 86 and 88 at the predetermined lead angle a as previously discussed.

Die blanks 12 and 14 may be additionally provided with a pair of keyways 92 in their base. Keyways 92 extend transverse to the longitudinal axis of the blanks and cooperate with keys 94 to maintain accurate alignment of the dies during the thread rolling operation.

With dies 12 and 14 in position, roll is pressed against the upper surface thereof and moved longitudinally in the direction T to cold-work the blanks and form a complementary configuration thereon. The spacers 90 are then removed from between the flat parallel faces 16 and 18 and bolts 17 tightened to move the dies 12 and 14 into abutting relation as seen in FIG. 3.

In order to form the unitary thread-rolling die 30 so that it can roll-form the screw 40 illustrated in FIG. 5, the ridges and grooves on crusher roll 10 must be similar in cross section to the threads and roots of screw 40. This is due to the fact that the roll must form ridges 60, grooves 62 and 64, and cavities 70, 70', 72 and 74 in die 30 which are complementary to the threads and lobes to be formed on screw 40.

As seen in FIG. 2, each of the annular ridges 100 in group 80 are shaped, in cross section, as a truncated triangle having a relatively wide crest 108 and evenly sloped sidewalls 102. Ridges 100 correspond in cross section to the truncated thread form 48 of screw 40 and the spacing s, between these ridges, is equal to the screw thread pitch.

The annular ridges 104 in group 82, which correspond substantially to full thread form 49 on screw 40, are also shaped in cross section as truncated triangles; however, these ridges have a greater height above cylindrical surface 84 and a narrower crest 106 than does ridges 100. The spacing s between ridges 104 is the same as that for ridges 100 and as will be more fully described hereinafter, this is necessary in order for the dies to form a single, continuous constant pitch thread on a cylindrical screw blank.

Ridges 100 and 104 of each group define grooves 107 therebetween of substantially equal width, and each of which lies on the cylindrical surface 84. Grooves 107 form the crests 60 on die blanks 12 and 14 during the rolling operation, and as previously noted these crests are complementary to the thread roots to be formed on the screw blanks.

Crests 108 of certain of the ridges 100 on roll 10 include sets of various sized cam-shaped protuberances or lobes 110,

' 110', 112 and 114 formed thereon which serve to roll-form the complementary sets of cavities 70, 70, 72 and 74 on die plate 12. Each set of lobes corresponds in cross section to one of the lobes 50, 50', 52 or 54 formed on screw 40 and as previously noted, each set of cavities on the die plate serves to form asingle lobe on the cylindrical screw blank during the rolling process. Each lobe on roll 10 is a generally elliptically shaped protrusion in plan which inclines inwardly from a thickened base portion to converge and form a linearly disposed surface 116. The lobes in set 114 have a wider base and extend outwardly further than those in the set 112 which, in turn, extend further than those in sets 110 and 110, and the lobes in the two latter sets are of substantially the same size.

When a cylindrical screw blank is rolled between thread rolling dies, any point on its surface moves in a plane parallel to the longitudinal axis of the die. Accordingly, since each set of cavities on die 30 will form a single thread-forming lobe on screw 40, these cavities must lie on a line parallel to the longitudinal axis of the die. Accordingly, since each set of cavities on die 30 will form a single thread-forming lobe on screw 40, these cavities must lie on a line parallel to the longitudinal axis. Thus, the lobes of each set, 110, 110, 112 and 114, must be located on roll 10 such that as the roll is moved over the angularly positioned blanks I2 and 14, they form sets of complementary cavities along straight longitudinally extending lines. To achieve this result, each of the lobes in a set is evenly spaced on the periphery of the roll so that corresponding points on each lobe of a set define a line inclined at an angle to the rolls longitudinal axis, equal to the lead angle a. For example, the bottom, as viewed in FIG. 2, of each lobe 114 defines a line AA that is inclined with respect to the longitudinal axis of the roll at an angle. In this manner, although ridges 60 and grooves 64 on die plates 12 and 14 are formed at an incline to the longitudinal axis of the plates, each of the cavities in a set, e.g., cavities 74a, b and c, lie along a line parallel to that axis.

As the crusher roll is moved over dies 12 and I4, ridges of group 80 form the truncated thread form section of the die on the face of blank 12, and ridges 104 of group 82 form the full form section of the die on blank 14. Since the threadforming lobes on the bolt must increase in size as they progress closer to the full thread form, the sets of lobes 110, 112 and 114 are arranged on the crusher roll so that set 74 of cavities are formed closest to die blank 14 than are the remaining cavities which are located progressive farther away from blank 14 as their size increases.

As described above, it has been found desirable to have a flat depressed zone 66 in the thread rolling die immediately prior to the first cavities engaged by the cylindrical bolt blank. The depth of zone 66 may be the same as the complementary truncated thread form grooves formed in the die by ridges 108 on roll 10. Accordingly, as seen in FIG. 2, section is provided over an arcuate portion of roll 10 in which no ridges are formed. Ramp sections 122 provide a smooth transition from cylindrical surface 84 to the arcuate surface 124 of section 120 which surface is at the same radial distance from surface 84 as the crests 108 of ridges 100. Surface 124 extends around to the backside of roll 10 (not seen) approximately the same distance as on the front side illustrated, and the backside roll 10 is identical to the front side seen in FIG. 2 except that no lobes are formed on the ridges 100 on that side.

The die-forming operation is substantially as follows: A pair of generally rectangular die blanks 12 and 14, clamped together along their abutting surfaces 16 and 18 by bolts 17, are separated by unthreading the bolts. Spacer blocks 90 having a predetermined length are placed between surfaces 16 and 18 and bolts 17 are tightened to clamp blocks 90 therebetween and to maintain the desired spacing. The die blank assembly is then placed in paths 86 and 88 defined by the dissimilar groups of serrations 80 and 82 on crusher roll 10. The blanks are inclined with respect to the path of travel of the roll at an angle equal to the lead angle of the threads to be formed. The crusher roll 10 is pressed against the blanks 12 and 14, and moved longitudinally in the direction T over the upwardly facing surfaces of the blanks. As the roll is moved, it rotates about its longitudinal axis 1 l and cold-works these surfaces of the blanks to form a configuration thereon which is complementary to the configuration of lobes and ridges on roll 10. After roll 10 has completely passed over blanksl2 and 14, bolts 17 are again loosened and the spacers 90 removed. Bolts 17 are then retightened to draw the blanks transversely towards each other and keys 94 insure proper alignment as the blanks are moved.

Since the spacing s between the ridges of each group 80 and 82 of ridges was the same, and since the spacing d between the blanks during the rotation of the crusher roll is a multiple of the pitch of the threads or spacing s when plates 12 and 14 are moved into abutment along their flat parallel faces 16 and 18, the ridges formed thereon by the grooves 106 on roll 10 will be aligned. It is due to this alignment of ridges on the completed die that a single, continuous pitch thread can be formed on bolt 40 since these ridges are complementary to the thread root on the bolt. As seen in FIG. 1, the group of ridges 80 will only engage blank 12 and the group 82 will only engage blank 14. By this construction the transition between different depth grooves in the two die plate sections 12 and 14 occurs along a line 125 parallel to the longitudinal axis of the die, i.e., the line defined by the abutment of sides 16 and 18. Thus, as the screw blank is rolled along the longitudinal axis of plate 30 in the roll forming process, each point on its surface will respectively engage a serration which is the same as the one previously engaged, to insure proper thread forming. In addition, the longitudinally extending transition line 125 serves to assure proper and accurate forming of transition thread 47 on screw 40.

In FIG. 6, there is illustrated a modified crusher roll 130 adapted to engage spaced die blanks 12 and 14. The structure illustrated therein is similar to that illustrated in FIG. 1 and like numerals are used to indicate like parts.

Roll 130 includes groups of ridges 80 and 82 as did roll 10, however, the groups are separated by a cylindrical member or undercut roll section 132 whose peripheral surface is in axial alignment with the cylindrical surface 84 which defines the base of grooves 106. Section 132 does not contact either of blanks 12 or 14 but acts merely as a spacer between groups 80 and 82, in lieu of the abrupt change between groups in roll 10 of FIG. 1, in order to insure that each group of ridges only contacts its associate blank. The axial length of this section must be a multiple of the ridge spacing s to insure that the ridges formed in the pair of die blanks by grooves 106 are aligned when the blanks are clamped together at the completion of the operation. The spacing d between blanks l2 and 14 must be increased to accommodate section 132, and as before, must also be a multiple of spacing s. In all other respects, the operation of this embodiment is the same as that of the embodiment of FIG. I.

It is thus seen that the present invention provides a method for making a single integral thread rolling die which is adapted to form self-retaining thread rolling screws of the character described.

It is to be understood that the foregoing disclosure of the preferred embodiment of this invention is illustrative and exemplary only, and that the invention is not limited to the specific embodiments shown and described since modifications and changes may be made therein without departing from the inventive concept.

What is claimed is:

l. A method of making thread rolling dies having dissimilar thread forms of like pitch comprising, the steps of, providing first and second longitudinally extending die blanks in spaced parallel relation, spacing said blanks a distance equal to a predetermined multiple of the pitch, positioning a crusher roller on one surface of each said blanks at an angle to the longitudinal axis thereof, pressing said crusher roller against said surfaces and rolling said roller along said surfaces whereby a complementary configuration is formed on said surfaces at an incline to the longitudinal axis thereof.

2. The method as defined in claim 1 including, the steps of, forming a generally straight edge on each of said blanks and positioning said blanks with said edges adjacent each other and in spaced parallel relation.

3. The method as defined in claim 2 wherein said step of spacing said blanks includes the steps of, inserting at least a pair of spacer blocks, each having a length equal to said predetermined multiple of pitch, between said straight edges and clamping said blanks against said blocks.

4. The method as defined in claim I including, the step of, moving said die blanks transversely towards each other, following said step of rolling, and clamping said dies in fixed abutting relation.

5. The method as defined in claim 3 including, the steps of, removing said blocks, after said step of rolling, and clamping said blanks in abutting relation along said adjacent straight edges. v

6. The method as defined in claim 5 wherein said step of clamping includes the steps of threading at least one screw in each of said plates to effect relative transverse movement therebetween.

7. The method as defined in claim 1 including, the steps of, forming first and second groups of laterally positioned annular ridges and grooves on said crusher roll corresponding respectively to said first and second blanks, wherein the annular ridges in said second group have a greater diameter than the annular ridges of said first group.

8. The method as defined in claim 7 including, the step of, forming a predetermined distribution of cam-shaped lobes on certain of said ridges in said first group whereby complementary cavities are formed in said first blank as said crusher roll is moved thereover.

9. The method of making thread roll dies adapted to form a thread rolling screw having a continuous pitch thread with a truncated thread form pilot end section, a full thread form section and thread-forming lobes on said pilot end, comprising the steps of, forming a first plurality of annular ridges and grooves on the cylindrical surface of a crusher roll corresponding substantially in cross section to the truncated thread form of the screw to be rolled, forming a predetermined distribution of various sized cam-shaped lobes on certain of said ridges, forming a second plurality of annular ridges and grooves on said cylindrical surface corresponding substantially in dimensions to the full thread form of the bolt to be rolled, whereby said first and second plurality of ridges and grooves define first and second adjacent and longitudinally extending traverse paths respectively, positioning a first die blank in said first traverse path with the longitudinal axis of said blank inclined to the longitudinal axis of said path, positioning a second die blank in said second path parallel to and tranversely spaced from said first die blank, pressing said crusher roll against said die blanks, rolling said roll along said adjacent longitudinally extending traverse paths to form ridges, grooves, and cavitieson one surface of said blanks, complementary to said ridges, grooves and lobes on said crushing roll, moving said blanks transversely towards each other and fixing said blanks in abutting relation along their adjacent parallel edges.

10. The method of making thread roll dies comprising, the steps of, forming first and second dissimilar thread form sections on a crusher roll, mounting said roller for rolling movement along a generally longitudinally extending axis whereby said first and second roll sections define first and second lon gitudinally extending paths respectively, positioning a first die blank in said first path at an angle to said axis, positioning a second die blank in said second path in spaced parallel relation to said first blank, rolling said crusher roll over said die blanks to produce dissimilar thread forms on said blanks, and joining said blanks along their adjacent parallel sides to form an integral thread roll die having diissimilar thread forms of like pitch.

11. The method of making thread rolling dies having dissimilar thread form sections of like pitch wherein the thread forms in said sections are positioned parallel to a longitudinally extending thread-forming path, comprising, the steps of, positioning a first die blank at a predetermined angle to said longitudinally extending path, positioning a second die blank in spaced parallel location to said first die blank, rolling a crusher roller simultaneously over one face of each of said 

1. A method of making thread rolling dies having dissimilar thread forms of like pitch comprising, the steps of, providing first and second longitudinally extending die blanks in spaced parallel relation, spacing said blanks a distance equal to a predetermined multiple of the pitch, positioning a crusher roller on one surface of each said blanks at an angle to the longitudinal axis thereof, pressing said crusher roller against said surfaces and rolling said roller along said surfaces whereby a complementary configuration is formed on said surfaces at an incline to the longitudinal axis thereof.
 2. The method as defined in claim 1 including, the steps of, forming a generally straight edge on each of said blanks and positioning said blanks with said edges adjacent each other and in spaced parallel relation.
 3. The method as defined in claim 2 wherein said step of spacing said blanks includes the steps of, inserting at least a pair of spacer blocks, each having a length equal to said predetermined multiple of pitch, between said straight edges and clamping said blanks against said blocks.
 4. The method as defined in claim 1 including, the step of, moving said die blanks transversely towards each other, following said step oF rolling, and clamping said dies in fixed abutting relation.
 5. The method as defined in claim 3 including, the steps of, removing said blocks, after said step of rolling, and clamping said blanks in abutting relation along said adjacent straight edges.
 6. The method as defined in claim 5 wherein said step of clamping includes the steps of threading at least one screw in each of said plates to effect relative transverse movement therebetween.
 7. The method as defined in claim 1 including, the steps of, forming first and second groups of laterally positioned annular ridges and grooves on said crusher roll corresponding respectively to said first and second blanks, wherein the annular ridges in said second group have a greater diameter than the annular ridges of said first group.
 8. The method as defined in claim 7 including, the step of, forming a predetermined distribution of cam-shaped lobes on certain of said ridges in said first group whereby complementary cavities are formed in said first blank as said crusher roll is moved thereover.
 9. The method of making thread roll dies adapted to form a thread rolling screw having a continuous pitch thread with a truncated thread form pilot end section, a full thread form section and thread-forming lobes on said pilot end, comprising the steps of, forming a first plurality of annular ridges and grooves on the cylindrical surface of a crusher roll corresponding substantially in cross section to the truncated thread form of the screw to be rolled, forming a predetermined distribution of various sized cam-shaped lobes on certain of said ridges, forming a second plurality of annular ridges and grooves on said cylindrical surface corresponding substantially in dimensions to the full thread form of the bolt to be rolled, whereby said first and second plurality of ridges and grooves define first and second adjacent and longitudinally extending traverse paths respectively, positioning a first die blank in said first traverse path with the longitudinal axis of said blank inclined to the longitudinal axis of said path, positioning a second die blank in said second path parallel to and tranversely spaced from said first die blank, pressing said crusher roll against said die blanks, rolling said roll along said adjacent longitudinally extending traverse paths to form ridges, grooves, and cavities on one surface of said blanks, complementary to said ridges, grooves and lobes on said crushing roll, moving said blanks transversely towards each other and fixing said blanks in abutting relation along their adjacent parallel edges.
 10. The method of making thread roll dies comprising, the steps of, forming first and second dissimilar thread form sections on a crusher roll, mounting said roller for rolling movement along a generally longitudinally extending axis whereby said first and second roll sections define first and second longitudinally extending paths respectively, positioning a first die blank in said first path at an angle to said axis, positioning a second die blank in said second path in spaced parallel relation to said first blank, rolling said crusher roll over said die blanks to produce dissimilar thread forms on said blanks, and joining said blanks along their adjacent parallel sides to form an integral thread roll die having dissimilar thread forms of like pitch.
 11. The method of making thread rolling dies having dissimilar thread form sections of like pitch wherein the thread forms in said sections are positioned parallel to a longitudinally extending thread-forming path, comprising, the steps of, positioning a first die blank at a predetermined angle to said longitudinally extending path, positioning a second die blank in spaced parallel location to said first die blank, rolling a crusher roller simultaneously over one face of each of said die blanks along said longitudinally extending path, said roller having first and second dissimilar thread configuration sections adapted to form complementary thread confiGurations on said first and second blanks, respectively, and joining said blanks along their adjacent parallel sides to form a single die having two dissimilar thread forms. 